Process for manufacturing heat exchangers



June 8, 1965 G. SCHOLL 3,187,415

B0 E S FOR MANUFACTURING HEAT EXCHANGERS Filed March 29, 1961 4 Sheets-Sheet 1 June 8, 1965 s. SCHOLL PROCESS FOR MANUFACTURING HEAT EXCHANGERS Filed March 29, 1961 4 Sheets-Sheet 2 INVENTOR. S l

June 8, 1965 G. SCHOLL 3,187,415

PROCESS FOR MANUFACTURING HEAT EXCHANGERS Filed March 29, 1961 4 Sheets-Sheet 3 FIG/2 INV EN TOR.

W SQLJK M 9 W June 8, 1965 G. scHOLL PROCESS FOR MANUFACTURING HEAT EXCHANGERS Filed March 29, 1961 4 Sheets-Sheet 4 F/GZZU FIG. 2/

INVENTORL gm): suu u BY 3,187,415 PROCESS FQR MANUFACTURHQG HEAT EXQHANGERS Giinter Schiill, 21 Mulhergerstrasse, Essiingen, Germany Filed Mar. 29, 1961, Ser. No. 99,197 Claims priority, application Germany, Apr. 4, 1969,

Sch 27,688 Claims. (Cl. 29157.3

The present invention relates to heat exchangers.

More particularly, the present invention relates to heat exchangers and a process and apparatus for manufacturing heat exchangers.

As is well known heat exchangers conventionally include a tube through which a fluid flows in order to give up or receive heat, and it is conventional to provide at the exterior surface of such a tube fins, ribs, pins, and the like so as to greatly increase the exterior surface of the heat exchanger. Of course, the construction of such heat exchangers is rendered relatively complex and expensive because of the necessity of attaching to the exterior surface of the tube elements of the above type for the purpose of increasing the heat exchanging material and the exterior surface of the heat exchanger.

It is accordingly a primary object of the present invention to provide a heat exchanger which will increase the exterior surface of a tube as well as the volume of material through which heat flows but which can be constructed far less expensively than conventional heat exchangers.

A further object of the present invention is to provide a heat exchanger as well as a process and apparatus for manufacturing the heat exchanger according to which any desired combination of characteristics for the elements located at the exterior surface of the heat-exchanging tube may be provided in a simple, inexpensive manner.

A further object of the present invention is to provide a process and apparatus for manufacturing a heat exchanger according to which elongated sections of a surface and volume increasing means are successively joined to a tube in a stepwise fashion.

It is also an object of the present invention to provide a process and apparatus capable of continually joining to a tube structure which increases the exterior surface and the heat-exchanging volume thereof while the tube continues to advance longitudinally.

It is furthermore an object of the present invention to provide a process and apparatus according to which elements such as the convolutions of the coil spring are welded to a tube in such a way that an impulse of welding current is automatically provided precisely at the instant when the pressure between the convolutions and the tube is at a maximum.

With the above objects in view the invention includes a heat exchanger made up of an elongated tube and a series of portions of convolutions of a coil spring distributed longitudinally along and welded to the exterior surface of the tube. According to the process of the present invention at least one coil spring has at lea-st one convolution pressed against a tube and welded thereto. The apparatus of the invention includes welding electrodes at least one of which engages the coil spring and is provided with grooves for receiving the convolutions of the coil spring, each of these grooves having a pair of opposed side surfaces which diverge from each other toward the exterior surface of the electrode so that the convolutions are wedged into the groove between the opposed side surfaces thereof The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be United States Patent 0 best understood from the following description of specific embodiments when read in connection with the accompany drawings, in which:

FIG. 1 is a fragmentary transverse sectional illustration of a pair of electrodes and a coil spring and a tube which are welded to each other by current which flows through the electrodes and the coiLspring and the tube;

FIG. 2 is a fragmentary top plan view of the structure of FIG. 1, one of the electrodes being shown in section in FIG. 2;

FIG. 3 is a transverse sectional view showing an arrangement for welding a pair of coil springs to a tube;

FIG. 4 is a fragmentary top plan view of the structure of FIG. 3;

FIG. 5 is a transverse section of yet another arrangement according to the invention for welding a coil spring to a tube so as to provide a heat exchanger;

FIG. 6 shows the structure of FIG. 5 at a stage of the process subsequent to that illustrated in FIG. 5;

FIG. 7 diagrammatically illustrates a process and apparatus for successively welding to a tube convolutions of a pair of coil springs which are continuously advanced with the tube during the manufacture of the heat exchanger;

FIG. 8 shows in transverse section one of the many pos sible embodiments of a heat exchanger according to the invention;

FIG. 9 illustrates a further embodiment of a heat exchanger according to the invention;

FIG. 10 illustrates yet another embodiment of a heat exchanger according to the present invention;

FIG. 11 shows a further embodiment of a heat exchanger according to the present invention;

FIG. 12 shows yet another embodiment according to which the convolutions have a triangular configuration;

FIG. 13 shows a special heat exchanger where the tube is of a relatively large cross-sectional area;

FIG. 14 illustrates one of the many possible combinations of difierent types of heat-exchanging elements with the tube;

FIG. 15 shows a heat-exchanging structure which may be formed from the structure shown in FIG. 8;

FIG. 16 shows a heat-exchanging structure which may be formed from a structure similar to that shown in FIG. 10;

FIG. 17 is a cross-sectional illustration of a tube and, coil spring welded to each other;

FIG. 18 is a sectional view taken along line 18-18 of FIG. 17 in the direction of the arrows;

FIG. 19 illustrates one possible construction of a groove for receiving a coil spring convolution;

FIG. 20 shows a further embodiment of a groove structure for receiving the convolution of a coil spring; and

FIG. 21 shows yet another embodiment of a groove construction for receiving a convolution of a coil spring.

Referring to FIGS. 1 and 2, it will be seen that the elongated metallic tube 2 which may be made of iron or any other ferrous metal, for example, is in engagement with the convolutions of a coil spring 1. The coil spring 1 is engaged by an electrode 3 of a welding apparatus, this electrode 3 being formed with a series of grooves 4 which receive consecutive convolutions of the spring 1 in the manner shown particularly in FIG. 2, so that in this way the convolutions are maintained at a regular distance from each other. The tube 2 simply rests in a longitudinal groove of the electrode 5. With this construction when the tube 2 engages the electrode 5 and the spring 1, while the latter is engaged by the electrode 3 in the manner shown in FIG. 2, and when a suitable pressure is provided between the spring 1 and the tube 2 by urging one of the electrodes toward the other, the welding current is turned on by manual closing, for example, of a suitable switch and the current flows simultaneously through all of the convolutions between the pair of electrodes and pressing against the tube 2, so that all of the convolutions are simultaneously welded to the tube 2. After the welding is completed the electrodes are moved apart from each other, or only one of the electrodes is moved away from the other, and then the tube 2' and the spring 1 are axially advanced by a-distance substantially equal to the length of the electrodes 3 and so as to locate between the electrodes the next series of consecutive convolutions of the spring 1 which are to be welded to the tube .2, and thereupon one of the electrodes again is urged toward the other with a force sufilcient to provide the desired pressure between the spring convolutions and the tube, and then the circuit is again closed so as to cause the welding current to flow and produce the simultaneous welding of the second series of consecuitve convolutions to the tube 2. In this way, in a stepwise fashion, it is possible withthe embodiment of the process and apparatus of the invention shown in FIGS. 1 and 2 to weld a spring l to the tube 2 in a series of steps during each of which a plurality of consecutive spring convolutions are simultaneously welded to the tube 2. Of course, the tube 2 with the spring ll welded thereto formsa heat exchanger where the spring it performs the function conventionally performed by fins, ribs, pins, or the like.

Th embodiment of the invention which is illustrated in FIGS. 3 and 4 includes a pair of electrodes 9 and Ill which are substantially identical with the electrode 3 FIGS. 1 and 2, each of the electrodes 9 and 19 being formed with a series of grooves similar to the grooves 4 for receiving the successive convolutions of a coil spring,

as is shown particularly in FIG. 4. With the embodiment of FIGS. 3 and 4 the electrodes 9 and Till are urged one toward another so as to press a pair of coil springs 7 and 8 against the tube 6 which is intermediate the coil springs 7 audit, and then the electrical circuit is closed, so that with the embodiment of FIGS. 3 and 4 a pair of coil springs 7 and 8 are simultaneously welded at diametrically opposed parts of the tube 6 to the latter.

While in the description above it has been pointed out that the electrodes are moved apart from each other and then the tube with the spring or springs are axially advanced, it is of course possible to bring about the stepwise placing of the successive sections of the coil springs between the electrodes in any other way. For example,-

after welding is completed the entire unit formed by the pair of electrodes and the spring-tube assembly may be axially advanced, and then the electrodes may be moved away from the welded assembly and returned to their original position where the process is again repeated.

In order to guarantee welding of the convolutions of the coil springs to the tube, the grooves 4 have the construction shown in FIGS. 19-2-1. Thus, the groove 4a of FIG. 19 has a substantially trapezoidal cross-section, while the groove 4b of FIG. 20 has a similar cross-section except that the opposed sides are convexly curved. The

groove 4c of FIG. 21 has a conicalcross-section. The convolution la of a coil'spring is shown in the several p (it through a smaller area at the places where the convolutions engage the tube, and thus the greater temperature will be at the areas of contact between the convolutions of the coil springs and the tubes so that welding will reliably take place at the areas where the coil springs have their convolutions in engagement with the tube. The electrodes themselves are made, for example, of copper, while the coil springs as well as the tubes are made of ferrous metals, so that in this way also welding of the coil springs to the electrodes themselves is reliably prevented. As was pointed out above, the electrical circuit which provides the welding current is not closed unitl the coil springs are pressed against the tube with a pressure which will provide good area of contact between the coil springs grooves la-4c of FIGS. 19-21, and it is apparent that with volutions Id at the place where it is located in the groove of the electrode, the area of contact 1d between each convolution and the tube 2a is necessarily smaller than the area of contact between the convolutions and the electrodes, so that in this way the electrical current must flow and the tube. Referring to FIGS. 17 and 18, the convolution lie of a coil spring is shown in FIG. 17 pressing downwardly against a tube 20. The material of the coil spring and tube are such that they will be deformed slightly at the places where convolutions of the coil spring engage the tube, and in accordance with the present invention the welded area F shown in FIG. 18 is at least twice as great as the area P of the cross-section of the wire which forms the coil spring. In this way a reliablefusion of the coil springs and the tubes to each other is guaranteed.

FIGS. Sand 6 illustrate successive stages in a further process according to the present invention for manufacturing a heat exchanger. As may be seen from FIG. 5 the coil spring 12 has convolutions which are of a diameter substantially greater than the diameter of the tube 11, and a coil spring and a tube are originally placed so that theiraxes substantially coincide with each other, and thus the tube 11 is located within the spring 12. Any suitable structure may be provided for supporting the coil springs and tubes as well as the electrodes as well as for moving them relative to each other. Thus, electrically non-conductive blocks may be provided for supporting the elements while they are welded to each other, and electrically non-conductive pins, for example, may be located in the ends of the tube so as to support the latter while the springs are being welded thereto.

As is apparent from FIG. 5 a pair of electrodes 13 and M are placed in engagement with diametrically opposed portions of the spring 12, these electrodes 13 and 14 extending substantially parallel to the common axis of the tube ll and the spring 112. The electrodes 13 and 14 are then moved toward each other, as indicated by the arrows in FIG. 5, and when they have moved toward each other by a certain distance the structureof FIG. 6 will be provided. It will be seen thatin FIG. 6 the convolutions of the spring 12 have been distorted so that these convolutions now have a substantially oval configuration, and furthermore the inner surfaces of the convolutions of the spring 12 are pressed against the exterior surface of the I tube 11. When the structure has the position shown in FIG. 6 the circuit is closed so as to cause welding of the convolutions of the spring 12 to the exterior surface of the tube 11. it will be noted that with the heat exchanger provided in the manner illustrated in FIGS. 5 and 6 it is the inner surfaces of the convolutions which are welded to the exterior surface of the tube 111, while with the em bodiment of FIGS. 1 and 2 as well as with that of FIGS. 3 and 4 his the exterior surfaces of the convolutions which are Welded to the tubes. 7

- FIGS. 1-4 as well as FIGS. 5 and 6 show a process and apparatus for welding coil springs in a stepwise fashion to a tube. FIG. 7 shows a process and apparatus for continuously welding convolutions of a coil spring successively to a tube while the tube and the coil springs continue to advance axially.

Referring now to FIG. 7, it will be seen that the structure 'for continuously manufacturing a heat exchanger according to the process of the invention'includes a pair of rotary electrodes 18 and 119 which turn in opposite directions, respectively, as indicated by the arrows in FIG. 7. These electrodes 18 and 19 are formed at their peripheries with grooves 21 adapted to receive the convolutions of the coil springs and 16, as indicated in FIG. 7, and these grooves 21 may have any of the constructions illustrated in FIGS. 19-21. The tube 17 as well as the springs 15 and 16 are guided for movement downwardly, as viewed in FIG. 7, and as the springs 15 and. 16 move between the pair of rotary electrodes 18 and 19 which are continuously rotated in the directions shown from any suitable source of power and with any suitable transmission. The springs 15 and 16 are pressed at their convolutions against the exterior surface of the tube 7 at diametrically opposed parts thereof, and a structure described below is provided to provide an impulse of electrical current precisely at the moment when the pressure between the convolutions and the tube is at a maximum. The spacing betweenthe electrodes 18 and 19 is such that when the springs 15 and 16 have their convolutions successively located along a line which passes through the centers of the electrodes 18 and 19, these convolutions will be pressed to the maximum extent against the pipe 17. The electrodes 18 and 19 are made, for example, of copper, and of course with this construction when both of the springs 15 and 16 have their convolutions pressed against the pipe or tube 17 and the circuit is closed, then the convolutions will be welded to the tube 17 Any suitable structure is provided for guiding the springs and a tube for continuous axial movement in the manner indicated in FIG. 7.

As is shown diagrammatically in FIG. 7, a lever 20 is supported for pivotal movement about a pivot axis 22 which extends parallel to the axis of rotation of the electrode 18, and the lever 20 has a free end which engages the periphery of the rotary electrode 18. Each time the free end of the lever 21) enters into one of the grooves 21 the spring 23 which is connected to the lever 20 turns it in a counterclockwise direction about the pivot 22, and in this way a contact 24 which is carried by the lever 20 and insulated therefrom moves into engagement with a cooperating contact 25 which is stationary and which is carried by a stationary body 26 of insulating material. These contacts 24 and 25 are located in the circuit from which current is derived for the electrodes 18 and 19, and when the contact 24 moves in this way automatically into engagement with the contact 25 the circuit is closed and an impulse of current is provided through the electrodes and springs to weld the latter to the tube 17. The arrangement is such that when the free end of the lever 20 enters into a groove 21, the convolutions of springs 15 and 16 are pressed with the greatest force against the exterior surface of the tube 17, so that the impulse of current is automatically provided precisely at this moment.

Thus, it will be seen that with the process and apparatus of FIG. 7 a heat exchanger having substantially the same construction as that of FIGS. 3 and 4 will be provided, but with the process and apparatus of FIG. 7 the manufacturing of the heat exchanger takes place continuously while with the embodiment of FIGS. 3 and 4 the manufacture takes place in a stepwise fashion.

A heat exchanger having the construction known in FIG. 8 may also be provided. This exchanger includes a tube 30 with the plurality of coil springs 31a-31d having their axes parallel to each other and to the axis of the tube 30, these coil springs being distributed about and welded to the tube 30 in the manner shown in FIG. 8. The structure of FIG. 8 is provided, for example, by providing pairs of opposed electrodes which cooperate with the pairs of diametrically opposed springs. Thus, one pair of electrodes similar to the electrodes 9 and 10, for example, will cooperate with the springs 31a and 31c to place the latter in engagement with the tube 30 so as to be welded thereto, while a second pair of identical electrodes will cooperate with the springs 31b and 31d.

The embodiment of FIG. 9 may be provided in much the same way. Thus, the several springs 32a-32d will be welded to the pipe 32 in the same way as described above in connection with FIG. 8. In addition, a third pair of electrodes similar to the electrodes 9 and 10 are provided to cooperate with the springs 33a and 33b to weld the latter to the tube 32 in the manner shown in FIG. 9. It is apparent, therefore, that any desired combination of coil springs may be welded to the tube so as to form a heat exchanger therewith.

With the arrangement of FIG. 10 the convolutions of the coil spring are flattened in the manner described above in connection with FIGS. 5 and 6, and with the arrangement of FIG. 10 the electrodes which are similar to the electrodes 13 and 14 have their alternate grooves inclined oppositely so as to provide the alternate convolutions which are not only flattened but which tilt in opposite directions as shown at 35 and 36 in FIG. 10, these convolutions 35 and 36 being welded at their inner surfaces to the tube 34, as described above in connectionwith FIG. 6. With the arrangements shown in FIG. 11, the tube 37 has the springs 38a-38d welded thereto in a manner shown in FIG. 11. These springs are joined to the tube 37 in a manner described above in connection with FIG. 8, and after being joined to the tube 37, the springs are placed between pairs of members which are urged toward each other so as to flatten the springs to give them the configuration as illustrated in FIG. 11, and with this arrangement the springs will of course havetheir convolutions extending to a greater degree away from the axis of the tube than is the case with FIG. 8, so that the structure of FIG. 11 may be more desirable for certain purposes.

With the embodiment of FIG. 12, the tube 39 which corresponds to the tube 34 of FIG. 10 again extends through the coil spring 49. Thus, the embodiment of FIG. 12 is made in a manner similar to the embodiments of FIGS. 6 and 10. However, with the embodiment of FIG. 12 the electrodes which cooperate with the spring 41) to press the same against the tube 39 deform the con volutions so that they will have the triangular configura tion ih ustrated in FIG. 12, and this configuration may also be more desirable for certain installations.

With the embodiment of FIG. 13 the tube 41 has the cross-section indicated in FIG. 13. Thus, the tube 41 has a much larger cross-section than any of the above-described tubes, and the tube 41 is provided with a pair of opposed flat parallel side wall portions to one of which the springs 42a-42c are welded and to the other of which the springs 43a-43c are welded. With this embodiment three banks of electrodes similar to electrodes 9 and 10 are placed one above the other and cooperate with the springs to press the same against the tube 41 and to weld them to the tube 41 when the circuit is closed. Thus, one pair of electrodes 9 and 10 will cooperate with the springs 42a and 43a, the intermediate set of electrodes with the springs 42!) and 43b, while the lowermost set will cooperate with the springs 42c and 430 and all the electrodes will be urged toward each other simultaneously to press the springs against the tube 41 so as to provide the structure indicated in FIG. 13.

With the embodiment of the invention which is illustrated in FIG. 14, the tube 44 has the coil springs 45a, 45b and 46a, 46b joined thereto at diametrically opposed portions thereof. Thus, the heat exchanger of FIG. 14 is essentially similar to that provided according to the process and apparatus of FIG. 7 or that of FIGS. 3 and 4. However, after the structure is provided suitable die members are placed in engagement with the coil springs so as to leave the alternate convolutions thereof circular and so as to flatten the remaining convolutions, and the result is that on one side of the pipe 44 the coil spring will have alternate convolutions 45a and 451) which are. alternately circular and flattened, While on the other side the spring will have alternate convolutions 46a and 46b which will alternately be flattened and circular. Thus, with the invention it is also possible to provide arrangement where the springs themselves individually have convo'lutions of different characteristics.

The embodiment of the invention which is illustrated in FIG. 15 may be made from the embodiment which is shown in FIG. 8, for example. Thus, after a structure as shown in FIG. 8 is provided the springs are cut through at their convolutions. Referring to P16. 15, it will be seen that the tube 47 has four series of portions of convolutions of four coil springs Welded thereto. Before the springs have the configuration shown in Fig. 15, they have the configuration illustrated in FIG. 8, and the structure of FIG. 15 is made in exactly the manner as described above in connection with FIG. 8. Thereafter the convolutions are cut so as to be provided with free ends, and the free ends of. each convolution are bent away from each other so as to provide the structure shown in PEG. 15. Thus, the portion 43a of one of the convolutions of 'one of the springs corresponding to the spring 31a of P16. 8 has free end portions which'extend substantial-1y at right angles to each other, and the remaining coil springs are treated in the same Way so as to provide the structure shown in FIG. 15 which may be highly desiralble in certain types of installations.

The embodiment of the invention which is illustrated in FIG. 16 may originally have the structure as shown in FIG. 6 or in FIG. 10 except that the successive convolutions which are flattened as indicated in FIG. 10 do not extend in oppositely inclined directions and instead are all aligned with each other. According to FIG. 16, the tube 49, after the successive convolutions of the coil spring are flattened and joined thereto, is treated so that the several convolutions are cut at diametrically opposed parts thereof. Then one of the convolutions after being thus cut at a pair of diametrically opposed parts shown at the top and bottom of FIG. 16 is bent so as to have a pair of portions Eda and whose free ends are curved in the same direction, and the next convolution after it has been cut at diametrically opposed parts has its free ends bent in the opposite direction so as to have the pair of portions 51a and 51b, and this type of heat exchanger again may be highly suitable for a'particu'lar installation.

Thus, it is apparent from the above description that with the process and "apparatus of the invention it IS possible to provide in an extremely inexpensive manner heat exchangers having the widest possible variety of construction so that in order toprovide a heat exchanger of a special construction adapted to a special purpose it becomes possible for the first time with the process and apparatus of the invention to provide a heat exchanger of a specialized construction in an extremely inexpensive and highly efiicient manner,

The embodiment of FIG. 7 provides an extremely inexpensive process and apparatus for manufacturing a heat exchanger. Thus, with pairs of electrodes as shown in MG. 4, for example, it is necessary to have a source of energyon the order of 1,600 kw. to provide the power necessary for causing welding to take place at the several 'useful application in other types of heat exchangers differing from the types described above.

While the invention has been illustrated and described as embodied in process and apparatus for manufacturing heat exchangers, it is not intended to be li ited to the stalls shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A process for manufacturing a heat exchanger comprising the steps of placing an elongated tube within an elongated coil spring whose'convolutions have a dia1neter substantially larger than that of the tube with the axes of the coil spring and tube coinciding; placing a pair of electrodes in engagement with diametrically opposed portions of the coil spring; and moving the electrodes one toward the other so as to deform the convolutions of the coil spring into a substantially oval configuration and so as to place limited portions of the convolutions at their inner surfaces in'engagement with the exterior surface of the tube for completing a circuit through said tube, convolutions and electrodes and thus causing the convolutions of the coil spring to be welded to the tube at the exterior surface thereof.

2. A process for manufacturing a heat exchanger comprising'the steps of placing an elongated metal tube within an elongated metal coil spring Whose convolutions have a diameter substantially larger than that of the tube with the convolutions of said spring surrounding and spaced from said elongated metal tube so as to be out of electrical contact with said tube; connecting the coil spring and the tube in an electric welding circuit; consecutively deforming consecutive convolutions of said coil spring into engagement at spaced portions of said coil spring with the exterior surface of said tube for completing the electric Welding circuit through the portions of engagement between said tube and said convolutions of said coil spring while continuously advancing the tube and the coil spring; and applying the welding current between the coil spring and the tube at the moment whenthe pressure between said spaced portions of the consecutive convolutions and the tube is at a maximum.

3. In a process for manufacturing a heat exchanger, the steps of placing an elongated metal tube within an elongated metal coil spring whose convolutions have a diameter substantially larger than that of the tube with the convolutions of said spring surrounding and spaced from said elongated metal tube so as to be out of electrical contact with said tube; connecting the coil spring and the tube in an electric Welding circuit; deforming the convolutions of said coil spring into engagement at spaced portions of said coil spring with the exterior surface of the tube for completing the electric welding circuit through the portions of engagement between said tube and said convolutions of said coil spring to thus cause not only engagement between said coil spring and said elongated tube but also simultaneously therewith the welding of said coil spring at said portions of engagement of said coil spring to said tube. 1

4. A process for manufacturing a heat exchanger comprising the steps of placing an elongated tube within an elongated coil spring whose convolution-s have "a diameter larger than that of the tube with the axes of the coil spring and tube coinciding; placing a pair of shaped electrodes one provided with a surface complementary to said tube and the other having a plane surface nor- 7 mal to the apex of said first mentioned surface, in engagement with diametrically opposed portions of the coil spring; and moving the electrodes one toward the other so as to deform the convolutions of the coil spring into configuration against said tube and to place the convolutions at their inner surfaces in engagement with the exterior surface of the tube for completing a circuit through said tube, coil convolutions and electrodes and thus causing the convolutions of the coil spring to be Welded to the tube at the exterior surface thereof.

5. A process for manufacturing a heat exchanger comprising the steps of placing a pair of electrodes respectively in engagement with diametrically opposite portions of a tube and a coil spring surrounding said tube and having an inner diameter greater than the outer diameter of said tube; advancing the electrodes one to- Ward the other so as to deform the convolutions of the coil spring into engagement with the tube to complete a circuit through said tube, coil convolutions and electrodes and thus cause Welding of the coil spring to the tube; and simultaneously with said deformation, angularly displacing circumferentially about the tube, adjacent convolutions of the coil spring with respect to each other.

References Cited by the Examiner UNITED STATES PATENTS 288,995 11/83 Gold 257-26217 10 1,516,430 11/24 Hess a- 257--262.17 X 1,716,743 6/29 Still 257 262.17 2,268,680 1/42 VonLinde 29 157.3 2,277,462 3/42 Spofiord 257262.17 2,298,249 10/42 Brown 219-81 2,403,070 7/46 Fulton 219-107X 2,550,965 5/51 Brown 219-81 2,584,189 2/52 Dalin. 2,655,352 10/53 Dalin 165-183X 2,956,335 10/60 Matheny 6ta1 29 1s7.3 3,000,084 9/61 Garland 29l57.3 3,020,027 2/62 Dumpleton 29 157.3 X

FOREIGN PATENTS 531,031 10/56 Canada.

748,179 4/33 France.

423,330 1/35 Great Britain.

W'HITMORE A. WILTZ, Primary Examiner.

HERBERT L, MARTIN, Examiner. 

3. IN A PROCESS FOR MANUFACTURING A HEAT EXCHANGER, THE STEPS OF PLACING AN ELONGATED METAL TUBE WITHIN AN ELONGATED METAL COIL SPRING WHOSE CONVOLUTIONS HAVE A DIAMETER SUBSTANTIALLY LARGER THAN THAT OF THE TUBE WITH THE CONVOLUTIONS OF SAID SPRING SURROUNDING AND SPACED FROM SAID ELONGATED METAL TUBE SO AS TO BE OUT OF ELECTRICAL CONTACT WITH SAID TUBE; CONNECTING THE COIL SPRING AND THE TUBE IN AN ELECTRIC WELDING CIRCUIT; DEFORMING THE CONVOLUTIONS OF SAID COIL SPRING INTO ENGAGEMENT AT SPACED PORTIONS OF SAID COIL SPRING WITH THE EXTERIOR SURFACE OF THE TUBE FOR COMPLETING THE ELECTRIC WELDING CIRCUIT THROUGH THE PORTIONS OF ENGAGEMENT BETWEEN SAD TUBE AND SAID CONVOLUTIONS OF SAID COIL SPRING TO THUS CAUSE NOT ONLY ENGAGEMENT BETWEEN SAID COIL SPRING AND SAID ELONGATED TUBE BUT ALSO SIMULTANEOUSLY THEREWITH THE WELDING OF SAID COIL SPRING AT SAID PORTIONS OF ENGAGEMENT OF SAID COIL SPRING TO SAID TUBE. 